1. Field of the Invention
The present invention relates to photochromic diarylethenes substituted with isoxazole group expressed in the following formula (1), which provide excellent dispersability with polymers, especially fluorinated diacrylate monomers capable of photopolymerization and are capable of giving a thin film, prepared therefrom, of superior photochromic characteristic and high mechanical strength with UV irradiation to be useful as optical recording material and photo switch, wherein R1 is a direct bond, O, or C1-C3 alkylene optionally substituted with fluoro; R2 is a hydrogen atom, (CR4H)nOH or C6(R5)mH1; R3 is selected from the group consisting of a hydrogen atom, phenylisoxazole, hydroxymethylisoxazole, acetyl, hydroxy, and phenyl; R4 is C1-C10 alkyl; R5 is chloro, nitro, bromo, or the same as R4; X and Y are independently O, N, or S; Z is methylene optionally substituted with fluoro or carbonyl; and n, m and l are an integer of 1 to 5.
2. Related Background Art
Since 1985, diarylethene compounds have been synthesized and known as photochromic compounds having excellent thermal stabilities (Japan Kokai Tokyo Koho; JP 3261781; J. Org. Chem., 1991, 49, 373). Since then, various derivatives have been synthesized and reported for their uses in reversible optical disc, erasable optical disc, photo switch for optical integrated elements, organic photosensitizer, photo-electrode and the like (Japan Kokai Tokyo Koho; JP 789954, JP 8245579; Takeshita, M; Uchida, K; Irie, M. Chem. Commun., 1996, 1807-1808).
Since the diarylethene compounds change their color with UV irradiation and return to the original color with light irradiation having different wavelength, various photochromic compounds are disclosed to be useful in the field requiring for colored state and decolored state (Japan Kokai Tokkyo Koho; JP 5222037, JP 5222035, JP 7242659).
A method for preparing optical recording film by coating with a solution of fluoro-substituted diarylethene compound such as 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene dissolved with polymer resin has been reported because it has high thermal stability and rapid coloring speed (J. Org. Chem., 1991, 49, 373). However, when this fluorinated diarylethene is dissolved into polymer resin, it has problems in preparation of uniform thin film due to poor dispersability and low photochromic effect for low concentration of fluorinated diarylethene in the resin. On the other hand, when high concentration of the fluorinated diarylethene is used to increase photochromic effect, prepared thin film may be unclear and phase separation can be occured during long storage. Therefore, the conventional photochromic compounds have drawbacks in inferior reliability and storage stability as optical recording materials. Especially, aggregation of conventional diarylethenes results in difficulties in reading and decoding of recorded signals because it gives scattering of data over repeated reversible cycles. In order to solve these problems were disclosed 1-(6′-acetyl-2′-methyl-benzo[b]thiophen-3′-yl)-2-(2″-methyl-benzo[b]thiophen-3″-yl)hexafluorocyclopentene having benzene ring and its derivatives. However, the dispersability is increased some degree but it is hardly regarded as having fully satisfactory sensitivity and photochromic property as photo recording materials (Japan Kokai Tokkyo Koho; JP 05-301873; Irie, M., M. Chem. Rev., 2000, 1685-1716).